This invention is related to the field of earthworking tools such as those used on machines for cutting rock or coal or machines for road building and road maintenance. For purposes of illustration, this invention will be shown and described with respect to a road planer, a particular type of road building and road maintenance equipment.
The tools with which this invention is most concerned are those tools comprised of a base, a block (sometimes called a lug), and a bit for contacting the working medium. The bit may be any one of several types which are well known in the prior art.
A normal consequence of utilizing tools is an abrasive working medium such as the earth is that the tools wear out and must then be replaced. The period of time during replacement is greater when the bits are tipped with a hard wear resistant material such as tungsten carbide.
The tools are attached to a rotor which rotates causing the bits to dig into the earth. Often, the base and block are welded to the rotor while the bit is removably attached to the block. In normal operation, only the bit has to be replaced. However, it is recognized that the block itself may also wear out or even break. In this circumstance, the whole machine must be shut down so that a welder may be located for the purpose of removing the old block and then installing a new one. There is considerable expense involved in allowing such an expensive machine to lay idle.
Thus, it is desirable to also make the block replaceable as is, for example, shown in U.S. Pat. Nos. 2,905,456; 3,820,849; and 4,180,292.
This only partially solves the problem since, if an underground obstacle is encountered, such as buried railroad tracks, manhole rings, expansion plates or deck plates on bridges, an abnormally high cutting load will be put on the bit, and the base itself may be ripped from the rotor. If this occurs, the machine will then have to be shut down and a welder will have to be located as before.
A way to remedy the situation is to make the base and block sufficiently massive so that, together, they can withstand the resultant cutting forces. This is shown, for example, in U.S. Pat. No. 3,749,449. A consequence of this design is that the rotor becomes very heavy due to the "beefed-up" base and block so that the force available for cutting action through the bit is somewhat reduced. Of course, such a design would also be more expensive.
An alternative to the problems of the prior art has been provided by the invention of this application.
Thus, it is an object of this invention to provide a base and block assembly that is both lightweight and durable.
It is another object that the base and block assembly be cost effective.
It is a further object that the block of a base and block assembly be replaceable and yet be rigidly held by the base when in operation
It is a still further object of this invention that the base of a base and block assembly be protected from abnormally high cutting loads.